Key Instruments
The LA instrument couples an ArF excimer laser microprobe at 193 nm (Geolas 102 from Microlas) with a sector field high-resolution HR-ICP-MS Element I from ThermoFinnigan or a 8900 Triple Quadrupole ICP-MS system from Agilent.
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Short description of instrument capabilities
U-Th-Pb multi-phase geochronometry of accessory minerals are performed on a routine basis for formation ages of magmatic and metamorphic rocks, structural and tectonic framework studies and detrital accessory minerals provenance analysis. U-(Th-)Pb analyses of ZIRCON and MONAZITE are performed routinely but the lab team can support you doing U-Th-Pb dating of other mineral phases such as Baddeleyite, Titanite and Rutile.
Analyses can be performed directly on thin or thick sections and on mineral separates embedded in epoxy mounts (see “Sample type and dimensions” below). The laser spot size can vary from 5 to 120 μm and the minimum laser spot size depends mainly on mineral internal structures (i.e. zoning, inclusions and fractures) and is mainly function of the geochronometer (the high Th content of monazite allows analyses with monazite 5 μm laser spot size.
Sample cell and laser spot size (μm)
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Please note that the microscope on the laser instrument is not as good as some of the petrographic microscopes. In particular cases locating specific spots to analyze can be tricky and time-consuming, especially on polished sections. Prior to analysis users should acquire as much as possible micro-photos (whit both transmitted and reflected light) and SEM images (Cl, SE and BSE images) that will help localize the accessory minerals. Images should be taken at different magnifications.
Sample types and dimensions
Petrographic thin sections (27x45mm) and epoxy resin cylinder (1 or 2 inchs in diameter and with a maximum thickness of 0.7 cm) of embedded minerals (e.g. zircon, monazite, titanite and rutile). The surface to be analyzed must be polished and cleaned (without coatings).
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Publications for major details
Multi-phase dating
Langone A. & Tiepolo M. (2015) - U-Th-Pb multi-phase approach to the study of crystalline basement : application to the northernmost sector of the Ivrea-Verbano Zone (Alps). Periodico di Mineralogia, 84, 3B, 633-655. http://dx.doi.org/10.2451/2015pm435
Monazite dating
Paquette J.L. & Tiepolo M. (2007) - High resolution (5 μm) U–Th–Pb isotope dating of monazite with excimer laser ablation (ELA)-ICPMS. Chemical Geology, 240, 222-237. http://dx.doi.org/10.1016/j.chemgeo.2007.02.014
Langone, A., Braga, R., Massonne, H-J., Tiepolo, M. (2011) - Preservation of old (prograde metamorphic) U–Th–Pb ages in unshielded monazite from the high-pressure paragneisses of the Variscan Ulten Zone (Italy). Lithos, 127, 68-85. http://dx.doi.org/10.1016/j.lithos.2011.08.007
Zircon dating
Tiepolo M. (2003) In situ Pb geochronology of zircon with laser ablation–inductively coupled plasma–sector field mass spectrometry. Chemical Geology, 199, 1-2, 159-177. http://dx.doi.org/10.1016/S0009-2541(03)00083-4